How do I jump start a car?

Jump starting is straightforward but the order matters, and the last connection is deliberately made away from the battery. A car battery can vent hydrogen, and the final connection is the one most likely to spark — so it's made at a distance from the gas.

Safety

What you'll need

• Jump leads rated for the vehicle
• A second vehicle with a good battery of the same voltage
• Gloves and eye protection (optional)
• Vehicle handbook

Step by step

1. Check the handbook for a designated jump-start point — many modern cars have one.Some cars have the battery in the boot with remote terminals under the bonnet. Using the wrong point can damage electronics.
2. Park the vehicles close but not touching, both switched off with handbrakes on.Touching vehicles create an unintended earth path. Keys out, everything electrical off in both.
3. Connect a red clamp to the positive (+) terminal of the flat battery.Positive is usually marked with a red cover. Check before connecting anything.
4. Connect the other red clamp to the positive terminal of the good battery.Make sure the free black clamps don't touch anything metal at any point.
5. Connect a black clamp to the negative (−) terminal of the good battery.This one goes on the terminal normally.
6. Connect the other black clamp to an unpainted metal point on the flat car's engine block or chassis.Not the flat battery's negative terminal. This keeps the final, spark-prone connection away from any vented hydrogen.
7. Start the working car and let it run for a few minutes.This puts some charge into the flat battery before you ask it to turn a starter motor.
8. Start the flat car. If it doesn't start within about 10 seconds, stop and wait a minute.Prolonged cranking overheats the starter motor and drains the donor battery.
9. Disconnect in exact reverse order, without letting clamps touch.Earth point, then good negative, then good positive, then flat positive.
10. Drive for at least 20–30 minutes to put charge back into the battery.Idling charges very slowly. If it won't start next time, the battery or the alternator needs attention.

Tips

• A portable lithium jump starter removes the need for a second vehicle entirely and is a genuinely useful thing to keep in a car.
• If the battery goes flat repeatedly, the battery is likely at the end of its life or the alternator isn't charging. Jump starting is a symptom treatment.
• Cheap thin jump leads often can't carry enough current for a larger engine. Buy leads rated above your vehicle's needs.
• Cold weather sharply reduces battery capacity, which is why flat batteries cluster in winter.

Common mistakes

• Connecting the final black clamp to the flat battery's negative terminal — That connection can spark, and it's the point where vented hydrogen is most concentrated.
• Letting the clamps touch each other — A direct short across a car battery produces enormous current and can cause burns or an explosion.
• Cranking continuously — Overheats the starter motor and flattens the donor battery.
• Ignoring the handbook on a modern car — Many have specific procedures and dedicated jump points; getting it wrong can damage expensive electronics.

Questions people ask